Well hell here's my theory: Heavier flywheels smooth a powerband, absolutely no question about it! Does it add power, absolutely not nor does it add torque. The rotating mass of the flywheel is used to transfer the power when off the throttle, maintains momentum. In all actuality a flywheel costs horspower, there's nothing free about spinning mass, it's about transfer of energy that was originally produced by your motor. Does it affect tractibility? absolutely, this is why banshee's do not fair well as mx'rs, they spin too much because of the powerband hit. A heavier flywheel can smooth this out. Spinning tires get you no where fast accept with the right tires and it's generally in the sand. This mod is popular among duners because it allows just that, spinning tires! The banshee is less affected by a lighter flywheel cause it is a twin cylinder and a 2 stroke at that. Combustion is continuously driving the crank. A single cylinder 4 stroke doesn't have that and requires momentum to carry it through to the next compression stroke.